Curable organopolysiloxane compositions are used in protective coating agents used for semiconductor elements in optical semiconductor devices such as photocouplers, light-emitting diodes, solid state image pickup elements, etc. Such protective coating agents for semiconductor elements must neither absorb nor scatter light when semiconductor elements emit light or receive light.
However, when cured products of compositions comprising organopolysiloxanes having at least two silicon-bonded alkenyl groups per molecule, organopolysiloxanes having at least two silicon-bonded hydrogen atoms per molecule, and platinum complexes are subjected to heating over extended periods of time, they tend to yellow over time, and the optical transmittance of the cured products deteriorates. In particular, semiconductor devices with semiconductor elements encapsulated in such cured products have been prone to decreased reliability.
Therefore, it is an object of the present invention to provide a curable organopolysiloxane composition capable of forming cured products of superior optical transmittance exhibiting little heat-induced yellowing over time and a semiconductor device of high reliability, in which semiconductor elements are encapsulated in a cured product of the composition.